Shrimp

All harvesters

	Density	Modularity
pre-closure	0.4872449	0.1742505
post-closure	0.5255102	0.1866189

Portfolio networks of shrimp harvesters

	Density	Modularity
pre-closure	0.3443878	0.08913881
post-closure	0.3741497	0.1011536

Changes in portfolios of shrimp harvesters

Entry and exit

Post closure, shrimp (css, csc), lobster-apprentice under 18 (lau), and elver dip net fyke 1 (e6) are replaced by menhaden (menc, menr), spat, and aquaculture, all of which are new license categories and don’t necessarily represent a shift in fisheries.

The proportion of licenses held by shrimpers didn’t appear to change dramatically by those who chose to continue in fisheries. Lobster was still the dominant target species by these harvesters.

Difference in difference estimator

Did the closure of the shrimp fishery impact the number of licenses held by harvesters?

# A tibble: 4 × 5
  term             estimate std.error statistic  p.value
  <chr>               <dbl>     <dbl>     <dbl>    <dbl>
1 (Intercept)         1.29     0.0595     21.8  2.29e-16
2 shrimp_harvester    1.24     0.0842     14.7  6.92e-13
3 closure             0.106    0.0876      1.21 2.39e- 1
4 did                -0.307    0.124      -2.47 2.16e- 2

According to the DiD estimator, the closure did negatively impact those shrimpers in a statistically significant way. It may be worth noting that a significant number of harvester left fisheries entirely after the moratorium and we may need to figure out a way to incorporate exit and entry in the difference-in-difference estimation.